The original single site catalysts of the mid 1980's, such as a metallocene catalyst, produced resin having a narrow polydispersity (Mw/Mn) typically in the range from about 2.5 to 3.5. Early on it was recognized that blending such resins could produce bimodal resins, each component having a narrow polydispersity and the blend having a broader polydispersity. It was felt such resins would provide a good balance of processability and physical properties such as resin toughness. There are an increasing number of patents and applications in this field.
U.S. Pat. No. 4,530,914 issued Jul. 23, 1985 to Ewen et al., assigned to EXXON Research & Engineering Co. teaches the use in the same reactor of two metallocene catalysts each having different propagation and termination rate constants for ethylene polymerizations. The patent does not teach the polymers prepared in the presence of a phenoxide ligand containing catalyst of the present invention.
U.S. Pat. No. 6,346,575, issued Feb. 12, 2002 to Debras et al., assigned to Fina Research S.A. teaches a method to make a bimodal blended polymer by polymerizing monomers in a first reactor in the presence of a metallocene type catalyst and them moving the resulting polymer to a second reactor and polymerizing additional monomer in the prior formed polymer. The patent does not teach using a catalyst having a phenoxide ligand as required in the present patent. Further the patent teaches away from physical blending as required by the present invention.
U.S. Pat. No. 6,309,997 issued Oct. 30, 2001 teaches an olefin polymerization catalyst using a phenoxide (preferably a salicylaldimine) ligand for use in the polymerization of olefins. The patent does not teach blending such resins with a resin made using a single site catalyst (representative catalysts contain at least one cyclopentadienyl type ligand).
U.S. patent application 2002/0077431 published Jun. 20, 2002 in the name of Whiteker discloses a process for the polymerization and oligomerization of olefins in the presence of a mixed catalyst system in a single reactor. The catalyst system as disclosed comprises a first component similar to the catalyst containing the phenoxide component of the present invention except that at least one of substituents R3, R4, R5, R8, R9 and R10 must have a Hammett σp value (Hansch et al., Chem Rev. 1991,91,165) greater than 0.2 (i.e. at least one of these substituents needs to be a sufficiently electron withdrawing group, (e.g. CF3, Br, etc.)). In the present invention, in the catalyst containing the phenoxide ligand, all of R3, R4, R5, R8, R9 and R10 are hydrocarbyl substituents which have a Hammett value of less than 0.2. Furthermore, the reference teaches away from the blending approach of the present invention.
The present invention seeks to provide a polymer blend (physical blend) having good physical properties which would make it suitable for numerous applications including pipe applications.